Clinical activity of avapritinib in ≥ fourth-line (4L+) and PDGFRA Exon 18 gastrointestinal stromal tumors (GIST)

• Published in: Journal of clinical oncology Vol. 37; no. 15_suppl; p. 11022
• Main Authors: Heinrich, Michael C., Jones, Robin Lewis, von Mehren, Margaret, Bauer, Sebastian, Kang, Yoon-Koo, Schoffski, Patrick, Eskens, Ferry, Mir, Olivier, Cassier, Philippe Alexandre, Serrano, Cesar, Tap, William D., Trent, Jonathan C., Rutkowski, Piotr, Patel, Shreyaskumar, Chawla, Sant P., Meiri, Eyal, Zhou, Teresa, Mamlouk, Khalid Kevin, Roche, Maria, George, Suzanne
• Format: Journal Article
• Language: English; Japanese
• Published: 20.05.2019
• ISSN: 0732-183X; 1527-7755
• DOI: 10.1200/JCO.2019.37.15_suppl.11022

Abstract only 11022 Background: Targeting oncogenic KIT and PDGFRA mutations revolutionized treatment of patients (pts) with advanced GIST; however, nearly all pts succumb to resistant disease. Avapritinib is a potent and selective kinase inhibitor with broad activity against oncogenic KIT/PDGFRA mutants, including PDGFRA D842V and other primary or secondary resistance mutations. Updated results from the phase 1 NAVIGATOR (NCT02508532) study of avapritinib in pts with advanced GIST are presented. Methods: Adult pts with unresectable PDGFRA D842V or other mutant GIST who progressed on imatinib and ≥ 1 other tyrosine kinase inhibitor (TKI) were treated with oral, daily, continuous avapritinib. Adverse events (AE) and response by mRECIST 1.1 per central radiology were assessed. Safety from the overall population (30-600 mg doses) and efficacy in the response evaluable 4L+ and PDGFRA Exon 18 (Ex 18) populations treated at the MTD (400 mg)/RP2D (300 mg) were analyzed. Results: As of 16 Nov 2018, 237 pts [172 KIT, 62 PDGFRA Ex 18 (56 D842V, 6 non-D842V), 2 PDGFRA N659K, 1 missing] were enrolled including 111 in the 4L+ population (primarily KIT, median 4 prior TKI) and 43 in the Ex 18 population (median 1 prior TKI). The 4L+ ORR was 22% [1 CR, 23 PR (1 pending)], and 52 SD with median duration of response (mDOR) of 10.2 months (95% CI: 7.2-NE). The Ex 18 ORR was 86% [3 CR, 34 PR (1 pending)] and 5 SD; mDOR was not reached (95% CI: 11.3-NE). Most AE were grade 1-2, most commonly nausea (63%), fatigue (58%), anemia (49%), periorbital edema (42%), diarrhea (40%), vomiting (40%), decreased appetite (38%), increased lacrimation (33%), peripheral edema (33%) and memory impairment (most common cognitive AE, 29%). 10% of pts discontinued due to a related AE. Grade 3-4 related AE ≥ 2% were anemia, fatigue, hypophosphatemia, hyperbilirubinemia, neutropenia, and diarrhea. Conclusions: Avapritinib has important clinical activity in pts with advanced GIST who have no effective therapies. The ORR and DOR of avapritinib in 4L+ exceeds that of approved 2 nd and 3 rd line therapies and shows unprecedented activity in D842V and other Ex 18 mutant PDGFRA GIST. Results suggest avapritinib has the potential to change the treatment paradigm of pts with advanced GIST. Clinical trial information: NCT02508532.